1. Field of Invention
This invention relates to an engine control system for changing the engine speed on an agricultural vehicle in response to a change in tyre pressure. More specifically the invention relates to such an engine control system on an agricultural tractor.
2. Description of Related Art
An agricultural tractor is used both on roads and in fields. The tyre pressure necessitated for work on a field is low, roughly 0.8 bar. The tyre pressure required on road is higher, roughly 2 bar.
Some agricultural tractors are fitted with an automatic control system which allows the driver to set the vehicle speed (that is the speed over ground) and other parameters associated with the vehicle whilst the control system automatically changes the engine speed and the transmission ratio simultaneously to reach the desired vehicle speed. Such a system reduces fuel consumption.
Field work may require high power and therefore the engine speed may be high, for example 2100 rpm. If the driver then returns to the road, with the automatic control system activated, the system would decrease the engine speed to roughly 1750 rpm. Since the tractor has moved from the field to the road, it is necessary to increase the tyre pressure. Since the air for the tyre pressure control is supplied by an on board compressor which is driven directly by the engine, the performance of the compressor is decreased and as a result it takes longer to inflate the tyres than if the engine speed was the same as that on the field. The driver must therefore remember to deactivate the automatic control system when inflating the tyres and re-activate it when inflation has finished. Often this can be forgotten.
It as an aim of the invention to provide an engine control system which overcomes the aforementioned problems.